(1) Field of the Invention
This invention relates to a method for the adjustment of a variable delay line, and more particularly to a method for fine adjustment of a variable delay line, capable of digitally varying a delay time in an ultra-high speed signal having a rise time of not more than 1 ns.
(2) Description of the Prior Art
Among the conventional variable delay lines for digital variation of delay time, there is counted a type which is so configured that by the use of switch means capable of selectively switching between a delay line element possessing a predetermined time aand a signal wiring presumably involving no delay time, the delay time difference between the above delay line element and the signal wiring will be digitally varied.
The adjustment of the value of variation in the delay time in such a variable delay line as described above is effected by increasing or decreasing, by an amount of the order of about 1 ns, the delay time of the former delay line element which possesses a predetermined delay time.
The recent advent of semiconductor devices capable of passing ultra-high speed signals have been encouraging actual adoption of ultra-high speed signals having a rise time of not more than 1 ns. In the circumstance, variable delay lines have been urged to fill the requirement that they should permit fine division of variable steps of delay time and highly accurate adjustment of values of variation proper to the fine division. For example, the accuracy of adjustment is required to be as high as the order of 1 to some tens of ps.
Since the aforementioned variable delay line mostly uses a delay line element of the lumped-constant type possessing a plurality of sections it is capable of permitting only rough adjustment of delay time and is hardly capable of providing accurate fine adjustment of the value of variation.